Preparation of alkaline earth metal cyanides by double decomposition



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l.. J. CHRISTMANN ET AL. 2,386,436 PREPARATION OF ALKALINE EARTH METAL CYANIDES YBY DOUBLE DECOMPOSITION Filed May l0, 1943 f Wfl A/a cz f CA, K5 fw rf@ I Ca (CA/)E @NH3 o a r v Caf/W2 san/infra W/ff/ Arx/3 ATTORN EY Patented ot. 9, 19%

PREPARATION F ALKALINE EARTH METAL CYANIDES BY DOUBLE DECOMIPOSITION Ludwig J. Christmann, Yonkers, N. Y., and A1- lred G. Haupt, Stamford, Conn., assignors to Ameri can Cyanamidl (lompany, New York,

N. Y., aoorporation of Maine f Application 10, 1943, Serial No. 486,348

The present invention relates to a These `compounds are adapted for a variety of uses, i'or example, calcium cyanide is a readily available source of hydrocyanic acid through decomposition when exposed to a moist atmosphere.

Consequently, the compound is applicable to such uses'a's i'umigation for the control and extermination of insects. Calcium cyanide is valso utilized in the mining industry, for example, in processes for the extraction of metals from their ores. Barium and strontium cyanides are of particular utility as cementation agents in fused salt baths for case-hardening iron and steel articles.

'I'he principal object of thisinvention is to provide a method whereby the alkaline earth metal cyanides may be readily obtained in a substantially pure form. A further object resides in a method for the production of the alkaline earth metal cyanides requiring only simple equipment with high emciencies. Other objects will appear hereinafter. V,

It has been found that the above objects may be attained by establishing a cycle .of operation which includes the steps of dissolving an alkali metal cyanide in an alcohol chosen from the group consisting of methyl and ethyl alcohol, adding an alkaline earth'metal chloride to the alcohol solution, removing the insolubles and recovering the alkaline earth metal cyanide from the solution.

The preferred system of recovering the alkaline earth metal cyanide may include the steps oi treating the solution with ammonia, separating the precipitated alkaline earth metal cyanide diammoniate from the mother liquor, deammoniating the same to produce the desired alkaline earth Yns metal cyanide and recovering alcohol and/or ammonia for return to the cycle.

A convenient method of carrying out the rabove A cycle oi' operation is shown in diagrammatic form.

in the accompanying ow sheet. When the meth od is used to produce the cyanide'ofcalcium, for example, one mole equivalent of sodium cyanide is dissolved in a sumcient quantity of substantially .dry methyl alcohol. One-hali mole 'equivalent of anhydrous calcium chloride is Athen added slowlyto the alcohol solution with continuous method of preparing alkaline earth metal cyanides.

washed with'i'netlwl alcohol and the washings added to the illtrate. The alcohol solution of cal- -cium cyanide is a light straw-colored liquid which is reasonably stable upon standing, particularly if maintained at low temperatures. n V

In the preferred form, dry ammonia gas is then introduced into the calcium cyanide solution, whereupon calcium ycyanide diammoniate is precipitated as a crystalline, grayish-white, readily :alterable solid, having a slight pinkish cast. Due to the comparatively high heat of solution ol ammonia in methyl alcohol, cooling of the mixture during the ammoniatlon is desirable, preierably to a temperature below 35C., to avoid undue azulmicv decomposition and darkening of the liquor.

Dry or substantially anhydrous reagents are preferred in thepresent method due to the'iact that moisture has a tendency to decompose the alkaline earth metal cyanides, particularly the calcium cyanide, with consequent. lessening o! yields.

Where anhydrous liquid ammonia is available,

this material may be used advantageously for the simple reason that its addition at this point tends to maintain ya desirably low temperature in the precipitating vessel.

While the use of ammonium hydroxide has a drawback in that it introduces water, yet in the case of concentrated ammonium hydroxide, only small quantitiesl of water would enter the reacting menstruum, which may not cause a sulilcient final yields to be entirely objectionfA lowering .of able.

The slurry ofy calcium cyanide diammoniate is then filtered 'and 'the diammoniate may be washed with methyl alcohol saturated with ammonia. When so washed, the combined nitrate and washings containing methyl alcohol, ammonia and residual calcium cyanide are treated with acorn-l pound which, through double decomposition with the residual calcium cyanide, forms an insoluble calcium compound and a soluble cyanide. Compounds Which may be used for this purpose are carbonates, and in particular, the alkali metal carbonates, e. g. sodium carbonate, which are added tothe mother liquor preferably in aqueous solution. The mixture is then illtered to remove Y the precipitated vcalcium carbonate. The nitrate ischarged into a stripping still equipped with a fractionating column and a condenser. The alcohol and ammonia passing from the fractionating column are condensed and separately returned to the cycle. The aqueous alkali metal cyanide residue is removedirom the still and may be processed so as to obtain the cyanide in a substantially pure dry form and thereafter returned to the cycle.

In the above step, the mother liquor from the diammoniate precipitation is thus treated for i the purpose of having present a. more` stable cyanide, namely, sodium cyanide, from which the alcohol can be distilled. When the mother liquor without treatment is heated t a temperature sufilcient to distill oil the alcohol, a reaction takes place between the residual calcium cyanide and the alcohol, forming impurities which carry over in the distillate.

. The calcium`cyanide diammoniate is then deammoniated by heating to produce the substantially pure calcium cyanide, and the evolved ammonia returned to the cycle. A temperature of v from 200 to 230 C. is required i'or rapid separation of the ammonia. Temperatures within the range oi' 180 to 325 C. are feasible. However,

care must be taken at the higher temperatures to avoid decomposition of the calcium cyanide The deammoniaticn may be carried out by heating the diammoniate under a partial vacuum to avoid the contact of air and particularly moisture, and to facilitate the removal of the evolved l ammonia.

the dissolutiony oi' the calcium cyanide therein. Recycling the mother liquor as such would therefore lessen the eillciency oi' the process. Furthermore, removal of the -ammonia by merely heating the mother liquor is unsatisfactory as azulmic decomposition takes place with the formation or impurities soluble therein which lessen the grade of the ilnal product if this liquor isused in a subsequent cycle. As a consequence, by recovering the cyanide, alcohol and ammonia separately from the mother liquor, interference `of one with the other or with the emcient operation of the entire cycle is avoided, while at the same time all values can thus be used in this or other processes.

Example Two moles o! sodium cyanide (103.2 g. of 95% NaCN) were dissolved in 1400 cc. of dry methyl alcohol. One mole of calcium 'chloride (111 g. of 14-mesh anhydrous CaCla) was added slowlyto the alcohol solution during a period of thirty minutes with continuous agitation and ice bath cooling to keep the temperature of the liquor below 30 C.. 'Ihe resulting slurry was stirred for an additional thirty minutes, then nltered and the sodium chloride illter cake washed with 200 cc. of dry methyl alcohol. The combined nitrate and washings were treated with ten moles of gaseous ammonia at the rate oi' two moles per hour with stirring and cooling to a temperature of about C. The resulting suspension o! calcium cyanide dlammoniate crystals was nltered,

y claims.

cium carbonate was illtered oi! and the nitrate charged into a stripping still equipped with a fractionating column and a condenser. The methyl alcohol and ammonia were distilled from the mixture leaving the aqueous sodium cyanide residue in the still. The methyl alcohol was condensed and recoveredsubstantiallv ammonia-free. The ammonia was subsequently recovered and recycled. The crystalline calcium cyanide diammoniate `was heated under a `partial vacuum for 4 hours at a temperature of from 200 to 220 C., and the evolvedy ammonia recovered The remaining product was a pale gray powder, analyzing 97.8% calcium cyanide.

Similarly, other alkaline earth metal cyanides may be prepared in substantially pure from uti lizing the alkaline earth metal chlorides, it being highly important that in the recycling of the alcohol, the ammonia be removed.

When ethyl alcohol is used in place of methyl alcohol in the process. a larger quantity will be required due to the lower solubility of the alkaline earth metal cyanides therein.

The operation as described, ailords a convenient` and reliable method yior producing high grade alkaline earth metal' cyanides.

While the invention has been described with particular reference to speciiic embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the lscope of the appended We claim:

l. A method of producing an -alkaline earth metal cyanide which includes the steps of dissolving an alkali metal cyanide in an alcohol chosen. from the group consisting of methyl and ethyl alcohol, adding an alkaline earth metal chloride to the alcohol solution, removing the insolubles, adding ammonia to the solution to precipitate an alkaline earth metal cyanide diam moniate, separating the precipitated alkaline earth metal cyanide diammoniate from the mother liquor containing alcohol, ammonia and re- 5 sidual alkaline vearth metal cyanide, deammonie ating the alkaline earth metal'cyanide diammoniate, separating a substantially ammonia-free alcohol from the 'mother liquor and returning the said alcohol to the cycle.

2. 'I'he method of claim 1 in which the alcohol and ammonia are anhydrous.

8. The method of claim 1 in which the alkaline earth metal chloride is added to the alcohol so lution maintained at a temperature not exc and the fiter cake washed with cc. oi' cold drymethyl alcohol saturated with ammonia. The combined nitrate and wash liquor containing methyl alcohol, ammonia and residual calcium cyanide was treated with a 5% aqueous sodium carbonate solution to convert the calcium cy- 4. The method ot claim 1 in which the solutionis treated with ammonia at a temperature not exceeding about 35 C.

5.' The method of claim 1 in which the alkalin earth metal cyanide diammoniate is deammoniated at a temperature within the range ot to 325 C.

6. The method of claim 1 in which alcohol and ammonia are vaporized from the mother liquor and a substantially ammonia-free alcohol condensed from said vapors.

7. The method of claim 1 in which prior to the lseparation oi' the substantially-ammonia-iree a1- cohol, there is added to the mother liquor a compound4 which through double decomposition with the residual `alkaline earth metal cyanide forms an insoluble alkaline earth metal compound and a soluble cyanide, and removing the insoluble alkalme earth metal compound. y

anide to sodium cyanide; The precipitated cal- 76 8. The method of claim 1 in which prior to the s 2,386,436 Vseparation of the substantially ammonia-free alcohol, there is addedv tothe 'mother liquor an.

y aqueous solution' of a carbonate, and removingthe Y precipitated alkaline earth metal carbonate. Y l

9. The Amethod oi claim 1 infvvhich'prlor to the separation of .thesubs'tantially ammonia-free alcohol, there is added to the mother liquoran aqueous solution/of sodium carbonate, and removing the precipitated alkaline earth metal carbonate. f,

10. A method of producing an alkaline earth metal cyanide which includes thevsteps o1' dissolvingv an alkali vmetal cyanide in an alcohol chosen 'from lthe 'group consisting of methyl and ethyl alcohol, addinganv alkaline earth metal chloride to the alcoholfsolutlon, removing the insolubles, adding ammonia to the solution to prea cipitate an alkaline earth metal vcyanide diamf moniate, separating the precipitated alkaline earth metal cyanide diammoniate' from the mother fliquor containingv alcohol.' ammonia and residual alkaline earth metal cyanide, deammof niating the alkaline earthmetal cyanide diammoniate and returning the ammonia therefrom to the'cycie, separating a substantially-ammonia-ireealcohol from the mother liquor andreturning the said alcohol tothe cycle.

11.s method or producing an alkaline earth metal cyanide whichincludes the steps oI- dissolving an alkalil metal cyanide 'in 'anvalcohol chosen fromthe vgroup consisting oiiueth'yl and V.ethyl alcohol, adding anv alkaline earthchloride to the4V alcohol solution, removing: the in-y 12. .A method o! producing calcium cyanide which includes the steps of dissolving sodium cyanide in methyl alcohol, *adding calcium chloride *to thealcohol solution, rejecting the insolubles,

precipitating calciumv cyanide diammoniate from vthe solution vwith substantially dry ammoniapltering the precipitated calcium cyanide vv`diam- 'y moniate from the mother liquor containing methyl alcohol. ammonia and residual calciumcya'nide.

adding aqueous sodium carbonate to the mother liquor and removing the precipitated calcium carbonate, distilllng the methyl alcohol and ammonia from the thus treated mother liquor. recovering the aqueous sodium cyanide from thestill residue, separately returning the methyl alcohol and ammonia to the cycle, heating the calcium Ycyanide diammoniate under partial vacuum at a temperature of from 200 to 220 C. and returning e the evolved ammonia to the cycle.

v 13. A method ofv producing an alkaline earth which includes the steps of dissolving sodium cyanide iii-methyl alcohol. adding calcium chloride to the alcohol solution, removing the insoluble and recovering calcium cyanide from the solu- 1' tion;

solubles,'adding ammonia to the solution to precipitate an alkaline earth metal cyanide diamf moniate, separating the precipitated alkaline earth metal cyanide diammoniate from' the mother liquor containing alcohol, ammoniafand'l residual kalkaline earth metal cyanide, separating* asubstantially ammonia-free alcohol from they mother` liquor and returning the said-jalcoholfto 5 thecycle, deammoniatinc the-alkaline-ear',tli'iiiet` a1 cyanide 'diammoniate recoveringtheammOnia from the mother liquor thejdeammonlation step and retuming the sameft'o the cycle.

-which includes the steps of dissolving, sodium cy, anide in methyl alcohol, adding calcium chloride to the alcohol solution, removing the insolubles, adding ammonia to the lalcoholic solution oi cal;

cium cyanide to precipitate calcium cyanide di! ammoniate andv d'eaminoniating the'calcium cyanide diammonia l v LUDWIG J. cnnrsmamr.

man G. HOUPT, a

15. Akmethod or producing calcium cyanide 

